Starting Oct. 30, voters should drop their ballots off at a voting center or 24-hour drop box instead of putting them in the mail.
Colorado Secretary of State Wayne Williams said that's the best way to ensure ballots get in on time.
Ballots must be in the hands of an election official by 7 p.m. Election Day, Nov. 6. Postmark dates don't count.
"I have worked very hard to provide funding for our county clerks to set up 24-hour drop boxes so voters can drop off their ballots any time of the day or night," Williams said in a news release. "In Colorado, we want to make it as easy as possible for people to vote."
Coloradans can register to vote in person as late as Election Day.
The Voter Service and Polling Centers across the state will be open through Election Day, except for Sunday, Nov. 4.
All voters who vote in person must provide identification.